He is found next to the excavation site. When first interacted with, he asks Ness for some food in order to continue working on the excavation.
Upon resuming his work, he complains about the amount of monsters on the cave.

His brother George later gives Ness the Diamond that Gerardo found while digging.

Trivia

Gerardo and his brother were named in the Japanese version after Shigesato Itoi's gold mining partner, Shouji Mochizuki.[1]